1. Field of the Invention
This invention relates to soldering methods and more particularly to a method of effectively soldering components together that have different compositions, such as metallic terminals to coated silica substrates.
2. Description of the Prior Art
Soldering components that have different compositions presents certain technical challenges. One example of this is the soldering of terminals made from metal, such as copper, brass, or plated steels, onto coated silica substrates, such as glass or ceramic. Two concerns that arise when soldering different materials together include the different rates of expansion of the materials and the re-crystallization of the silica based substrate.
Prior art soldering technology requires that the glass be relatively cool for the heated terminal""s solder interface to solidify. This causes the cooled solder joint to contract and pre-stress the soldered interface, thereby reducing the mechanical strength of the connection. One specific example involves the soldering of copper electrical terminals to the silver oxide painted defrost grid of an automobile""s rear window, as shown in FIG. 1. The rate of expansion for the glass, is approximately 0.000004 inches per degree Fahrenheit, compared to 0.000009 inches per degree Fahrenheit for copper. This becomes a problem when the components are heated and cooled for the solder interface to bond the components together. During heating, the copper terminal will expand more than the glass. During cooling, the solder joint will solidify while the terminal contracts a greater amount than the glass. This causes the fully cooled terminal to exert stress on the solder interface and the glass, reducing the mechanical strength of the connection. This problem is evident in several other applications, including the soldering of electrical connection pins to dense silica monolithic circuit chips.
Prior art soldering methods tend to generate an excessive amount of heat when the heat for soldering is applied. Oftentimes, such soldering methods will generate sufficient heat to anneal tempered safety glass. Safety glass is tempered by first heating it to a critical temperature, then rapidly cooling it below a specific temperature. During the soldering process, the copper terminal is heated to cause the solder to flow, allowing the terminal""s heat to be transferred to the adjacent glass. This becomes a problem when the terminal""s solder temperature reaches or surpasses the annealing temperature of the glass. During cooling, the solder joint will solidify and the glass adjacent to the terminal becomes annealed. This annealed section of the glass will no longer be safety tempered and will no longer break into the small fragments required by Federal Regulations.
Therefore, there is a need for an improved method and system for soldering components together that are composed of different materials.
A method and system for rapidly soldering a solder-coated terminal to a structure, having a different material composition than the terminal, is disclosed herein. The system comprises an intense heat source, such as an intermittent micro flame, a terminal gripper, having gripping jaws that are comprised of a heat-conductive material, and an optional air-jet cooler.
The terminal is first secured between the jaws of the gripper, which are further adapted to selectively position the terminal closely adjacent the structure. Intense heat is applied to the terminal, in this instance being solder-coated, causing the solder to melt. The jaws are sufficient in thermal conductivity to serve as a heat sink, preventing the temperature of the terminal to significantly increase beyond the solder melting point during heating. This minimizes the transmission of heat from the terminal and layer of molten solder to the structure. After the solder has melted, the intense heat source is shut off and an optional jet of cool air is directed to the terminal. While the jet of air is cooling the terminal and layer of solder, the gripping jaws continue to remove residual heat from the terminal. These methods of cooling cause the solder joint to rapidly solidify.
Using this method and system, the time required to first melt the solder layer and then solidify the solder connection is short enough that the effect of the different rates of expansion between the terminal and the structure is greatly minimized. This is of great importance when the terminal-receiving structure is made of glass, such as tempered safety glass. The rapid heating and cooling time aid in preventing the safety glass from annealing and further allows for a stronger solder contact.
Therefore, a principal object of the invention is to provide an improved system for instantaneous heat sink soldering.
Still another object of the invention is to provide a system for instantaneous heat sink soldering that reduces the heat transfer from a heated metallic terminal to a silica/glass structure.
Still another object of the invention is to provide a system for instantaneous heat sink soldering that reduces the time required for solidifying the molten solder.
Yet another object of the invention is to provide a system for instantaneous heat sink soldering that will not anneal a tempered glass structure to which a metallic terminal is soldered.
Still another object of the invention is to provide a system for instantaneous heat sink soldering that minimizes the effect of the difference in the rate of expansion between a metallic terminal and a silica/glass structure when the two structures are soldered together.
These and other objects will be apparent to those skilled in the art.